From our previous experiments it may be concluded that teratogenic factors such as drugs and other chemical compounds not only affect the central nervous system of the embryo during early stages of development causing gross malformations, but also during later phases of brain and cerebellar development. The abnormalities produced in the latter group are of cellular nature, are frequently subtle in character and will reveal themselves morphologically as abnormal migration patterns, abnormal neuronal differentiation or lack of neurons as a result of cell death or abnormal matrix cell proliferation. Functionally the abnormalities may reveal themselves as behavioral, learning or motor disturbances. Based on previous observations the aims of the proposed experiments are: a) to study which factors control the interkinetic migration of matrix cells in the neuroepithelial zone and how neuroblasts migrate from the neuroepithelial zone to the periphery of the cortex under normal and abnormal conditions. b) to examine the differentiation of specific neurons and its processes in the cerebellum and neocortex after treatment of the matrix cells with small doses of 5-azacytidine and 5-bromodeoxyuridine. c) to determine the repair mechanism of the matrix cells in the neuroepithelial zone of the cerebellum and neocortex after a short term treatment with FUdR and to examine the effect of trauma and repair on the cytoarchitecture of the postnatal cerebellum. d) to explore the postnatal behavioral, learning and motor disturbances produced by prenatal treatment of the brain on days that highly specific neurons are formed by the matrix cells.